The Great Mortality: An Intimate History of the Black Death, the Most Devastating Plague of All Time

by John Kelly

In Europe, where the most complete figures are available, in many places the plague claimed a third of the population; in others, half the population; and in a few regions, 60 percent. The affliction was not limited to humans. For a brief moment in the middle of the fourteenth century, the words of Genesis 7—“All flesh died that moved upon the earth”—seemed about to be realized. There are accounts of dogs, cats, birds, camels, even of lions being afflicted by the “boil,” the telltale bubo of bubonic plague. By the time the pestilence ended, vast stretches of the inhabited world had fallen silent, except for the sound of the wind rustling through empty, overgrown fields.

To many Europeans, the pestilence seemed to be the punishment of a wrathful Creator. In September 1349, as the disease raced toward an anxious London, the English king Edward III declared that “a just God now visits the sons of men and lashes the world.”

Almost everywhere in Europe there was war, overpopulation (relative to resources), economic stagnation and decline, filth, overcrowding, epidemic (nonplague) disease, and famine, as well as climatic and ecological instability.

Trade and human expansion, the twin anthems of modern globalization, have opened up ever more remote areas of the globe, while transportation has enhanced the mobility of both men and microbes incalculably.

And for all the triumphs of modern science, infectious disease retains the ability to render us as impotent as our medieval ancestors.

According to the Foster scale, a kind of Richter scale of human disaster, the medieval plague is the second greatest catastrophe in the human record. Only World War II produced more death, physical destruction, and emotional suffering, says Canadian geographer Harold D. Foster, the scale’s inventor.

accounts of environmental instability appeared in the decades prior to the Black Death. In the West as well as the East, there were reports of volcanic eruptions (Italy), earthquakes (Italy and Austria), major floods (Germany and France), a tidal wave (Cyprus), and swarms of locusts “three German miles” long (Poland).

Assessing the Japanese deployment of a plague weapon against the Chinese city of Changteh early in the war, an admiring U.S. Army report notes that “one of Ishii’s greatest achievements . . . was his use of the human flea, P. irritans. . . . This flea is resistant to air drag, naturally targets humans, and could also infect the local rat population to prolong the epidemic. . . . Within two weeks [of the attack] individuals in Changteh started dying of plague.”

Most of the time Y. pestis and the rodent kingdom live in a state of unhappy but workable coexistence. The scientific term for the modus vivendi is enzootic. Animals continue to get sick and die, but usually there are enough partially resistant rodents in any given community to keep the smoldering embers of infection in check. There are a number of theories about why, from time to time, this biological firewall suddenly collapses and the colony is consumed by the flames of an epizootic—a full-scale outbreak of plague. These include genetic change in the plague bacillus, which makes it more virulent, and demographic changes in the wild rodent community, which make its members more vulnerable to plague. A third theory, not incompatible with the first two, is that epizootics are activated by surge years—sudden, dramatic spurts in the rodent population. No one is sure what causes surges, but a number of scientists believe that they may be related to sun spots, which follow roughly the same cyclical pattern as surge years in many (though not all) rodent species, approximately ten to twelve years.

In the case of rodents, one component of the pruning mechanism may be an alteration in the community’s genetic composition. As rodent numbers spike during the surge, the pool of older, partially immune animals—the community firewall—is diluted by a rapidly expanding group of younger animals who have not yet acquired resistance to Y. pestis. This pool of unprotected young may constitute the biological equivalent of an oil slick; throw a match on it and it bursts into flame.

In one thirty-four-year period on the eastern steppe, four of five plague outbreaks occurred in tarabagan surge years, and the victims were local hunters, men schooled in the dangers of trapping sick animals.

The Great Famine, the collective name for the crop failures, was a tremendous human tragedy. A half-million people died in England; perhaps 10 to 15 percent of urban Flanders and Germany perished; and a large but unknowable segment of rural Europe also succumbed. Devastating as the Great Famine was, however, it was only a harbinger of things to come.

The regional outbreaks of the disease that occurred after the Black Death—the epidemics of 1366–67, 1373, 1374, 1390, and 1400—all took place in periods of dearth. More centrally, the profound malnutrition of the Great Famine years may have left millions of Europeans more vulnerable to the Black Death. “A famine of . . . three years is of sufficient length to have devastating long-term effects on the future well being of human infants,” says Princeton historian William Chester Jordan, who points out that malnutrition often impedes proper immune system development, leaving the young with lifelong susceptibility to disease.

However, one thing even the Black Death could not change was human nature. Florentines responded to the pestilence in ways that still sound familiar. “Some people,” says Boccaccio, “were of the opinion that a sober and abstemious mode of living considerably reduced the risk of infection. They, therefore, formed themselves into groups and lived in isolation from everyone. Having withdrawn to a comfortable abode, . . . they locked themselves in and settled down to a peaceable existence, consuming modest quantities of delicate food and precious wines and avoiding all excesses. “Others took the opposite view and maintained that an infallible way to ward off this appalling evil was to drink heavily, enjoy life to the full . . . gratifying all one’s cravings . . . and shrug the whole thing off as one enormous joke.” Members of this group visited “one tavern after another drinking all day and night to immoderate excess or . . . they would do their drinking in various private houses, but only in ones where the conversation was restricted to subjects that were entertaining or pleasant. . . . People behaved as though their days were numbered and treated their belongings and own persons with abandon.” A third group of citizens “steered a middle course . . . living with a degree of freedom sufficient to satisfy their appetites, and not as recluses. They therefore walked about, carrying in their hands flowers or fragrant herbs or divers sorts of spices, which they frequently raised to ...